Field of the Disclosure
The present subject matter relates to devices for adjusting the spacing between adjacent vertebral bodies.
Description of Related Art
The spacing in the disc space between adjacent vertebral bodies may decrease for any of a number of reasons, including traumatic impacts and degenerative diseases. Improper spacing between adjacent vertebral bodies can lead to varying degrees of discomfort and/or pain and, if severe enough, may be reason for surgical correction of the spacing. Surgical correction often involves placement of an inter-body implant to support the vertebrae and restore the disc height to (or close to) its original height. To determine the proper size of the implant to place into the disc space, the current practice involves the use of traditional manual sizing paddles, which are often in the form shown in FIG. 1. Such known disc paddles S are generally oval-shaped, with one dimension H (referred to herein as its height) that is greater than another dimension W (referred to herein as its width). The distal end of the paddle S is inserted into the disc space in a flat orientation (i.e., with the plane of the paddle height H oriented parallel to the endplates of adjacent vertebral bodies) and then it is rotated 90° to re-orient the plane of the paddle height H perpendicular to the endplates. The height H of the paddle S is selected to equate to the proper separation between the adjacent vertebral bodies, such that the edges of the re-oriented paddle S contact the endplates and force proper spacing within the disc space. To accommodate different spacing situations, a set of paddles is typically provided with a variety of heights H, which may range from 8 mm to 14 mm in 1 mm increments.
One disadvantage to such an approach is that the means for delivering the distal end of the paddle S to the disc area (e.g., a working cannula) must be large enough to accommodate the height H and the width W. Accordingly, a relatively large delivery cannula or means is required to accommodate the larger-sized paddles. Larger paddles also require a larger access site, resulting in greater surgical resection and more retraction of nerve roots and other surrounding structures. This can lead to the possibility of greater trauma, loss of blood, and pain, as well as potentially increased surgical and recovery time. Nerve root retraction is one of the largest potential sources of patient harm in such procedures, and excessive retraction can lead to temporary or even permanent neural dysfunction. Another disadvantage is that each paddle is appropriate for only one separation amount, so if a particular paddle is initially used and found to result in improper spacing, it must be removed and the process repeated with a paddle having a different height. The multiple tool exchanges inherent in such an iterative sizing procedure increases the risk of damaging nerve roots or other surrounding structures.